Today, July 10, Sanofi Pasteur published in The Lancet the results of the first of two Phase 3 clinical trials for its dengue vaccine candidate — a live attenuated chimeric tetravalent vaccine. The study is a randomized, observer-blind, placebo-controlled multicenter trial involving 10,275 children aged 2 to 14 years in Indonesia, Malaysia, the Philippines, Thailand and Vietnam.

An Initial Examination of Results

The data from this trial showed moderate efficacy of 57% against any virologically-confirmed dengue and that efficacy against serotypes 1, 2, 3 and 4 is 50%, 35%, 78% and 75%, respectively. Vaccine efficacy was statistically significant for all serotypes except serotype 2. The reason behind variable vaccine efficacy is still unknown, inviting further in depth examination and analysis.

The efficacy against severe dengue or dengue hemorrhagic fever which leads to hospitalization was estimated to be 67% in the age group that was studied between the ages of 2 and 14 in the five countries in Asia, which is an encouraging result.

This trial also further reassures the safety of CYD-TDV in the first 12 months following the primary vaccine series, as results showed no signals of an increase in serious adverse events in the trial during the two years following the administration of vaccine.

Follow-Up: A Fuller Assessment

A fuller assessment of the efficacy of the vaccine will help us better understand the performance of this dengue vaccine candidate.

However, these results help us better comprehend the complexities and challenges of developing a dengue vaccine. They help pave the way for further research in the dengue vaccine development community.

Additionally, the results of the second pivotal efficacy trial in Latin America, which will be available at the end of 2014, will help complement these data from Asia and provide a wider lens of analysis for a global vaccine.

In the meantime, other vaccine candidates continue to advance through the pipeline. Two of them, one developed by Takeda, and another one by the U.S. National Institutes of Health and the Butantan Institute in Brazil, are currently undergoing Phase 2 trials. Merck, with ISCOM, and GlaxoSmithKline, with the Oswaldo Cruz Foundation, are conducting Phase 1 trials of their own vaccine candidates

Currently, no cure or treatment exists for dengue. As dengue cases rise — putting nearly half of the world’s population at risk — so does the urgent need for a preventive intervention. A safe, effective and affordable dengue vaccine would represent a major advance for the prevention of this disease and alleviate its burden on low and middle-income countries, where the disease is endemic.

For a full Q&A by the World Health Organization (WHO), please click here.